fix(wallet-auth): preserve signed upload form field names

[Osraka]

Motivation

Closes #2001

UploadContext.fields is an opaque signed multipart field map. Its generated schema explicitly tells callers to submit every entry unchanged, but wallet-auth responses are camelized by default. That rewrites valid field names such as success_action_status to successActionStatus, so the SDK can return a different upload context from the one supplied by the API.

All four wallet-auth helpers that return an UploadContext are affected: drop item media, drop allowlist, collection image, and profile image uploads.

Solution

Disable response camelization only for those four upload-context helpers. Other wallet-auth responses keep their existing camelCase behavior, and the profile image request keeps its existing snakeizeBody: false behavior.

The regression coverage verifies both response shapes used by the API:

• a single upload context through the real fetch boundary
• an array of upload contexts through the real fetch boundary
• all four helper call sites opt out of response camelization

Validation:

• npm run build
• npm run check-types
• npm run lint (passes with the existing unrelated Function warning)
• npm test (48 files, 1009 tests)